Must be between 20 and 25kg in mass, andHave a maximum less minimum capacity of no more than 4MJ.

The technologies that are available are the batteries, which they have been using since 2009, flywheels, which some have been developed for motorsport but not utilised in F1, or supercapacitors, which may, or may not, have been used by RBR.

First question is whether the full MJ capacity could be met given the weight restrictions?

Would having the ability to store a full 4MJ actually be desireable? The rules state maximum 4MJ stored, maximum 4Mj used per lap (from the ES to the MGU-K) and maximum 2MJ recovered per lap (MGU-K to ES). Some have suggested, in the past, that on one lap the driver may forego using the 2MJ he stored such that he could use the 4MJ on the next lap. But since you are expecting to recover 2MJ on that lap, would you need to store any more than 2MJ?

With the operation of the new power units energy stored will, most likely, be used almost immediately - either on the acceleration from the corner, or on the next straight. How much storage would actually be required?

Also, how vital is the ES in its link to the power unit? That is, will the ES be supplied by the engine manufacturer or the constructor? If one team opted for a different ES technology or supplier would it make a noticeable difference to the PU performance?

I believe the KERS prior to this was around 20kg+ total. so its quite the bump in size.

And i am sad to hear that they are forced to run minimum 20kg of energy storage. Let the development be a natural one. If its faster it will prove itself through racing.

If they are able to recharge completely during braking on one lap that could give us some interesting racing. You could modulate throttle to balance the car during braking.

I doubt they will hit more than 2MJ before they are able to cram that into the minimum weight storage. I believe this because i believe aero is still the dominant factor over the KERS abilities.ES = energy storage? Power Unit?

I think ES is still free. Never once heard anything else. Same for the PU. i believe the prior PUs where about 4-6kg largely depending on efficiency. giving 60kW.

So is there a limit on recovery or storage from the MGU-H? If there is a storage limit of say 2MJ/lap that would still allow the ES to be charged from 0 to 4 MJ in a single lap (2MJ from MGU-K and 2MJ from MGU-H).

If the MGU-H is permitted to recover more than 2MJ/lap (but not store it), can the surplus energy be sent directly to MGU-K to help drive the wheels?

It would make sense to have the ES fully charged whenever strategically desirable (impeding overtaking) and that would be easy to do by pulling some energy from the MGU-H anywhere on the course that max power is not required. Of course fuel efficiency will suffer and that will be a fascinating part of the juggling act.